1. Field of the Invention
The present invention relates to a cathode ray tube, and more particularly, to a cathode ray tube having a ferrite core with a modified sectional configuration to facilitate correction of a mis-convergence along a diagonal direction of a screen, to improve deflection efficiency, and simplify a process of manufacturing a ferrite core.
2. Background of the Related Art
FIG. 1 illustrates a related art color cathode ray tube.
Referring to FIG. 1, a related art color cathode ray tube includes a front glass panel 1 and a rear glass funnel 2 having a screen part fastened to the front glass panel 1 to form a vacuum tube. A fluorescent screen 13 is formed on the interior surface of the front glass panel 1 and an electron gun 8 is mounted to a neck part of the rear glass funnel 2 and oppose the fluorescent screen 13 for emitting electrons and thereby generate electron beams. A deflection yoke 9 is directly coupled to the neck part of the rear glass funnel 2 for deflecting electrons within the electron beams. Generally, the deflection yoke 9 includes a pair of horizontal deflection coils 21 for horizontally deflecting electrons within the electron beams; a pair of vertical deflection coils 22 for vertically deflecting electrons within the electron beams; a conically shaped ferrite core 24 for minimizing loss in the strength of a magnetic field generated by current flowing within the horizontal and vertical deflection coils 21 and 22, to thereby improve the efficiency with which the electrons are deflected (i.e., deflection efficiency); and a holder 23 for insulating the horizontal and vertical deflection coils 21 and 22.
Upon operation of the aforementioned color cathode ray tube, electrons within the electron beams are deflected by the deflection yoke in horizontal and vertical directions wherein the deflected electrons strike the fluorescent screen 13 on the front glass panel 1 to display a predetermined color image.
FIG. 2 illustrates a cross sectional view of a related art deflection yoke 9 shown in FIG. 1 taken along line A–A′.
Referring to FIG. 2, circular shaped horizontal deflection coils 21 are wound around an interior surface of the holder 23 having a circular cross section while circular shaped vertical deflection coils 22 are wound around an external surface of the holder 23. Further, the conically shaped ferrite core 24 is coupled to the external surface of the vertical deflection coils 22.
Upon operation of the related art deflection yoke 9, a current having a frequency of at least 15.75 KHz flows within the horizontal deflection coils 21 and induces a magnetic field capable of horizontally deflecting electrons within the electron beams. Further, a current having a frequency of 60 Hz flows within the vertical deflection coils 22 and induces a magnetic field capable of vertically deflecting electrons within the electron beams.
Generally, electrons within the electron beams are deflected via a deflection yoke 9, incorporating a self-convergence system, wherein a non-uniform magnetic field converges three electron beams (R, G, and B electron beams) generated by the electron gun 8, onto a screen without the use of extra circuits or devices. By adjusting the winding configuration (or turn) of the horizontal and vertical deflection coils 21 and 22, respectively, the self-convergence system generates barrel or pin-cushion shaped magnetic fields around portions of the deflection yoke 9 proximate the front glass panel 1, around portions of the deflection yoke 9 proximate the neck part of the funnel 2, and around central portion of the deflection yoke 9, wherein, based on their un-converged positions, the three electron beams are deflected differently to a predetermined region on the front glass panel 1. Use of the aforementioned horizontal and vertical deflection coils 21 and 22 typically are not sufficient to deflect electron beams to the predetermined region on the screen, thereby necessitating use of the aforementioned ferrite core 9.
The ferrite core 9 has a high magnetic permeability and minimizes the loss in the strength of the magnetic field in its the return path through the core 9 and consequently enhances the magnetic force of the deflection coils.
FIG. 3 illustrates a portion of the rear glass funnel 2 to which a RAC type deflection yoke is installed.
Referring to FIG. 3, the interior or exterior cross sections of the related art rear glass funnel 2, coupled to a RAC type deflection yoke, gradually changes from a substantially circular shape at the neck part to a substantially non-circular shape at the screen part (e.g., rectangular shape). The shape of the rear glass funnel 2 ensures that electron beams drawing a rectangular shaped raster on the fluorescent screen 13 form a rectangular shaped pattern within a passing region where the electron beams pass through the deflection yoke coupled to the rear glass funnel 2. Accordingly, the portion of the deflection yoke 9 proximate the screen part of the rear glass funnel 2 often has a rectangular cross section to improve deflection efficiency. Further, the portion of the ferrite core 24 proximate the screen part of the rear glass funnel 2 is also provided with a rectangular cross section. Providing the deflection yoke 9 and the ferrite core 24 with the aforementioned cross sections reduces power consumption of the deflection yoke 9.
FIG. 4 illustrates a related art RAC type deflection yoke having a rectangular cross section.
Referring to FIG. 4, the cross section of the deflection yoke 9, the interior and exterior cross sections of the ferrite core 24, and the cross sections of the horizontal and vertical deflection coils 21 and 22, respectively, are rectangular. The current required by the horizontal and vertical deflection coils 21 and 22, having rectangular cross sections as shown in FIG. 4, to deflect electrons within the electron beams is less than the current required by the horizontal and vertical deflection coils 21 and 22 having the substantially circular cross section as shown in FIG. 2, since the deflection coils shown in FIG. 4 are closer to the electrons within the electron beams than the deflection coils shown in FIG. 2.
For example, the distance between the electron beams and the horizontal and vertical deflection coils 21 and 22 in the deflection yoke having the rectangular shaped cross section is about 20% less than the distance between the electron beams and the horizontal and vertical deflection coils 21 and 22 in the deflection yoke having the substantially circular shaped cross section. As a result, the deflection efficiency of the deflection yoke 9 having the rectangular shaped cross section is increased by at least 15–20% over the deflection efficiency of the deflection yoke 9 having the substantially circular shaped cross section.
Deflection efficiency may be enhanced when the ferrite core 24 having the rectangular shaped cross section is included with the deflection yoke 9 having the rectangular shaped cross section. Accordingly, the interior surface of the rectangular ferrite core 24 is characterized by a horizontal interior surface diameter and a vertical interior surface diameter, different from the horizontal interior surface diameter. As the interior surface of the ferrite core 24 includes different diameters, the ferrite core must be processed with greater precision than that required to fabricate the ferrite core 24 shown in FIG. 2. Accordingly, an increased amount of time and money are required during a grinding process capable of increasing the size precision of interior surface of the ferrite core 24. Consequently, a production yield of the ferrite core 24 having the rectangular cross section is, at best, 50% of the production yield of the ferrite core 24 having the substantially circular cross section resulting in the unit price of the ferrite core 24 having the rectangular cross section being twice of the unit price of the ferrite core 24 having the substantially circular cross section.
To overcome the aforementioned problems with the RAC type deflection yoke, a Round Core Tetra Coil Combined deflection (hereinafter referred to as RTC) type deflection yoke has been proposed. The RTC type deflection yoke combines the horizontal and vertical deflection coils having the rectangular cross section as shown in FIG. 4 with the ferrite core including interior and exterior surfaces with the substantially circular cross section as shown in FIG. 2.
While the deflection efficiency of the RTC type deflection yoke 9 is 4–5% lower than that of the RAC type yoke including the deflection yoke 9 and ferrite core 24 with the rectangular cross sections as shown in FIG. 4, the RTC type deflection yoke 9 may be manufactured with reduced difficulty and reduced cost.
FIG. 5 illustrates a portion of an RAC type deflection yoke including a ferrite core, horizontal deflection coil, vertical deflection coil, and holder, each having a rectangular cross section while FIG. 6 illustrates a portion of an RTC type deflection yoke including a ferrite core having a substantially circular cross section and a horizontal deflection coil, vertical deflection coil, and holder each having a rectangular cross section.
Referring to FIG. 5, in RAC type deflection yokes, the cross section of the portion of the ferrite core 24 proximate the screen part of the rear glass funnel 2 (hereinafter referred to as the screen part of the ferrite core 24) is rectangular as are the cross sections of the deflection coils 21 and 22 such that a vertical distance 31 between the ferrite core 24 and the vertical (deflection coil 22, a diagonal distance 33 between the ferrite core 24 and the vertical deflection coil 22, and a horizontal distance 32 between the ferrite core 24 and the horizontal deflection coil 21 are all substantially the same.
Referring to FIG. 6, however, in an RTC type deflection yoke, the cross section of the portion of the ferrite core 24 proximate the screen part of the ferrite core 24 is substantially circular while the cross sections of the deflection coils 21 and 22 are rectangular such that the diagonal distance 33 between the ferrite core 24 and the vertical deflection coil 22 is less than the vertical distance 31 between the ferrite core 24 and the vertical deflection coil 22 as well as the horizontal distance 32 between the ferrite core 24 and the horizontal deflection coil 21 while the vertical and horizontal distances 31 and 32 are substantially the same. As a result, the strength of diagonally oriented magnetic fields becomes greater than the vertically and horizontally oriented magnetic fields. Consequently, a mis-convergence phenomenon occurs wherein deflections of the R, G, and B electron beams deviate along diagonal directions.
FIG. 7 illustrates the manifestation of the mis-convergence phenomenon in a related art RTC type deflection yoke.
Referring to FIG. 7, because the strength of diagonally oriented magnetic fields are generally greater than vertically and horizontally oriented magnetic fields in RTC type deflection yokes, vertically directed mis-convergences (e.g., PQV(−) and S3V(+)) and a horizontally directed mis-convergence (e.g., PQH(−)) are often observed at diagonal regions (e.g., corner regions) of the screen.